CN101065915A - Bias-control for optical mach-zehnder modulators with voltage-induced optical absorption - Google Patents

Bias-control for optical mach-zehnder modulators with voltage-induced optical absorption Download PDF

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CN101065915A
CN101065915A CNA2005800266199A CN200580026619A CN101065915A CN 101065915 A CN101065915 A CN 101065915A CN A2005800266199 A CNA2005800266199 A CN A2005800266199A CN 200580026619 A CN200580026619 A CN 200580026619A CN 101065915 A CN101065915 A CN 101065915A
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compensating signal
signal
arm
mzm
mach
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CN101065915B (en
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许平杰
迈克尔·C.·拉尔森
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Viavi Solutions Inc
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Flex Products Inc
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0121—Operation of devices; Circuit arrangements, not otherwise provided for in this subclass
    • G02F1/0123—Circuits for the control or stabilisation of the bias voltage, e.g. automatic bias control [ABC] feedback loops
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure
    • G02F1/2257—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure the optical waveguides being made of semiconducting material
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/21—Thermal instability, i.e. DC drift, of an optical modulator; Arrangements or methods for the reduction thereof

Abstract

A bias-control circuit that provides operating point control for a Mach-Zehnder modulator experiencing optical absorption at their interferometric arms. The bias control circuit generates compensation signals that are used to counter the thermally induced index shifts as a result of absorption. In addition, an operating point with desirable transmitter characteristics can also be arbitrarily chosen by over-compensating or under-compensating thermal effects.

Description

Bias voltage control with optics Mach-Zehnder modulator of voltage induced optical absorption
The cross reference of related application
The application requires the rights and interests of the U.S. patent application of following common pending trial and common appointment according to 35U.S.C. part 119 (e):
By the U.S. Provisional Patent Application sequence number 60/598 of Ping-Chiek Koh in submission on August 5th, 2004,938, title is " BIAS-CONTROL FOR OPTICAL MACH-ZEHNDER MODULATORS WITHVOLTAGE-INDUCED OPTICAL ABSORPTION, ", and the agency is numbered 122.48-US-P1;
This application is come in by reference is combined at this.
Statement about the development project of federal funding
The present invention is by being given by AUS aviation and missile command, and based on contract the government-funded of W31P4Q-04-C-R072 is researched and developed.Government has inevitable right to the present invention.
Technical field
The present invention relates generally to a kind of Mach-Zehnder (Mach-Zehnder) modulator, more specifically, relate to a kind of bias voltage control with optics Mach-Zehnder modulator of voltage induced optical absorption.
Background technology
(note: the application is with reference to many different publications, these publications in whole specification by being included in for example [x] expression of reference number in the bracket.According to the tabulation of these different publications of these reference numbers ordering below title find in the part of " bibliography ".Each of these publications in this combination as a reference).
Mach-Zehnder modulator (MZM) is operated by modulating two optical phase differences between the waveguide, the long mutually then or Modulation and Amplitude Modulation (AM) of destructive interference to realize exporting of these two waveguides.Their routines are by lithium niobate (LiNbO 3) material makes.
These LiNbO 3MZM is the essential element in the contemporary optics communication system.In different configurations, these modulators can demonstrate good emitting performance, High Extinction Ratio for example, low insertion loss, high frequency band width and low transient chirp (lowtransient chirp).These required characteristics cause LiNbO 3MZM uses in analog-and digital-optical communication system on a large scale.
Yet in order to keep good emitting performance, the phase difference between two waveguides must be accurately controlled so that offset the influence of environmental change or component ageing.Thereby, need the bias voltage control loop to offset the slow variation of average phase-difference.The bias voltage control loop produces direct current (DC) compensating signal, and it keeps MZM to work near the point on its transmission characteristic.
To LiNbO 3The DC bias voltage control loop design of MZM is set up in the prior art well.Control loop is generally taked the form of the low frequency AM shake of radio frequency (RF) drive signal for MZM, detects this narrow audio range frequency component of output, and regulates the DC bias voltage the low frequency output signal is remained on zero place.
Because the demand for capacity constantly increases, therefore need to reduce cost, power consumption and the packing forms (footprint) of all elements.Laser and modulator mutual encapsulation had good effect aspect packing forms that reduces transmitter and the cost in single component, but only can realize [1,2] by the monolithic of laser and modulator is integrated further reducing aspect size and the power consumption.This may cause semiconductor MZM, for example based on the research and development of the MZM of indium phosphide (InP).
Fig. 1 is the block diagram of typical semiconductor MZM100, this MZM comprises optics input 102,1 * 2 multi-mode is interfered (MMI) coupler 104, relative to each other has two modulator arm 106,108 of 0 ° or 180 ° of (PI) phase delay or skew respectively, M0 on the arm 106 (0 °) electrode 110, M0 phase place on the arm 106 (0 °) electrode 112, the MP on the arm 108 (180 °) electrode 114, the MP phase place on the arm 108 (180 °) electrode 116, and 2 * 2MMI coupler 118, it is the output of MZM100.Two outputs 120,122 of 2 * 2MMI coupler 118 are called as DATA120 and DATABAR_TAP122.DATA output 120 is coupled to one or more output optical fibres 126 by collimating lens 124 optical fiber, and optical tap 128, and DATABAR_TAP output simultaneously 122 is coupled to a power tap photodiode 130.By voltage being applied in the modulator arm 106,108, being changed by eq effect by the phase difference between two light waves of arm 106,108 propagation, and being converted into Strength Changes as the result who interferes in output place.This produces theoretical sinusoidal electric light (E/O) transfer function, and wherein when MZM100 was used as intensity modulator, it located work at point (differential phase of PI/4).
As mentioned above, the emission characteristics in order to be consistent in over a long time generally needs the MZM control loop for example to drift about to offset various effects, the aging and variations in temperature of element, and these effects stop MZM always to work at the point place.The use of control loop is crucial among the MZM, and the scheme of control LiNbO3MZM roughly can be divided into two types:
(a) based on the LiNbO of distortion 3MZM control, the ratio that it seeks to minimize even level item (general the 2nd grade) and fundamental frequency causes MZM always in the work of the point place [3,4] of E/O transfer function.This controlling schemes is used the following fact: at the point place, Taylor's series expansion has non-zero odd level item, and all even level items are all zero.General realization is F by using the frequency that is applied to bias voltage mThe dither signal by a small margin at place is finished.Use photoelectric detector so that opto-electronic conversion and the detection little variation as dither signal result's optical power to be provided.The fundamental frequency of measuring detection signal is (at frequency F mThe place) and the 2nd grade (at frequency 2 * F mThe place) amplitude of component.Controlling schemes seeks to change bias voltage so that minimize the 2nd grade of the supervisory signal ratio with fundamental frequency.
(b) control [5] based on the amplitude-modulated MZM bias voltage of RF drive signal.This controlling schemes is used the symmetry characteristic of sinusoidal E/O transfer function, so that in that put equidistant any 2 slopes of locating from integration operation identical.Thereby owing to disappear mutually each other at the given symmetric property in point place in the out-phase AM at optics one-level and optics zero level place modulation, Modulation and Amplitude Modulation (AM) electrical input signal at integration operation point place will cause at AM frequency (F mHz) locate detected minimum amplitude.General realization is F by apply frequency on the gain controlling of the RF of MZM amplifier-driver mThe low-frequency jitter of Hz is finished.Optical signalling utilizes photoelectric detector tap and detection, and based on opto-electronic conversion, measuring frequency is F mThe amplitude at Hz place.Because the AM at optical grade place no longer causes desirable disappearing mutually, therefore any and departing from of point all will cause the increase of the amplitude that detects, thereby controlling schemes seeks to change integration operation point so that detection signal is in minimum value.
Based on LiNbO 3MZM and the main difference between the MZM of based semiconductor be that in semiconductor MZM, voltage induced phase shift and electric absorption take place simultaneously.This absorption of light wave becomes non-linear relation with voltage usually, and causes the heating of MZM arm.
Thereby, semiconductor MZM and LiNbO 3MZM is inequality aspect main at two:
(1) the E/O transfer function is no longer corresponding to common SIN function.
(2) electric absorption causes photoelectric current, thereby causes the heating of MZM arm.This causes that the thermal induction optical index moves, and it complicates the operation of semiconductor MZM and control.
(1) and the implication of (2) be based on above-mentioned (a) and controlling schemes (b), it will have difficulties aspect the appropriate control signals producing, this signal can be used for bias voltage semiconductor MZM so that its normal running.
Under the situation of (a), half-power point that E/O transmits and the point with maximum slope efficient overlap no longer each other, need to be out of shape with control to minimize the 2nd grade of scheme with the ratio of fundamental frequency harmonics.The frequency that depends on dither signal, controlling schemes also must be handled any additional influence of moving the result as the thermal induction index.
For (b), heat number is shown and moves the one-sided AM optics output that causes for the zone of reasonableness of extinction ratio with experimental technique.Fig. 2 shows and utilizes PI phase shift semiconductor MZM as an example, produces the physics reason of one-sided AM optics output when the optics electric absorption exists.Fig. 2 A is the curve chart of electricity input, and B is the curve chart of E/O transmission and electric absorption and input voltage relation, and C is the curve chart of optics output and electricity input A.Utilize the Modulation and Amplitude Modulation drive signal shown in Fig. 2 A, except the modulated optical power amplitude, also modulate by absorbing the thermal induction index that is caused and move, particularly at the voltage place that absorbs slope corresponding to height.This thermal induction index moves the transfer curve that has changed modulator, makes it absorb the slope region place at height and changes in the out-phase mode with respect to the Modulation and Amplitude Modulation drive signal.The Modulation and Amplitude Modulation drive signal at low absorption edge place is followed the tracks of in the displacement of out-phase transfer curve now, cancel or significantly reduce the optics Modulation and Amplitude Modulation, thereby cause side AM modulation output, wherein tap and E/O switching signal will show no longer that any minimum signal is for the control loop locking.This acts on shown in Fig. 2 B and Fig. 2 C.
Therefore, there are the needs that improve semiconductor MZM control.Clearly, owing to the distortion of normal sinusoidal transmission characteristic, have the needs of following controlling schemes, this controlling schemes can prevent that the bias voltage control loop from controlling to the faulty operation point improperly.In addition, because heat and Modulation and Amplitude Modulation effect are interfering with each other nocuously, therefore have the needs of following controlling schemes, this controlling schemes can prevent to cause that with the simultaneous heating of optical absorption control loop can not be at the bias voltage semiconductor MZM of action required point place.The present invention satisfies these needs.
Summary of the invention
The present invention is a kind of bias control circuit, and described bias control circuit provides operating point control for the Mach-Zehnder modulator of interfering arm place experience optical absorption at it.This bias control circuit produces compensating signal, and described compensating signal is used to offset the thermal induction optical index that is caused by described optical absorption and moves.In addition, the operating point with required emission characteristics also can be selected arbitrarily by overcompensation or undercompensation thermal effect.This technology can be applicable to have or do not have the Mach-Zehnder modulator of absorption.
Description of drawings
With reference now to accompanying drawing,, in the accompanying drawings, identical Reference numeral is represented corresponding part in whole specification:
Fig. 1 is the block diagram of typical semiconductor Mach-Zehnder modulator.
Fig. 2 shows and utilizes PI phase shift MZM as an example, when having the optics electric absorption, utilizes bilateral AM modulation electric input signal to produce one-sided AM optics output.
Fig. 3 A is the figure of Modulation and Amplitude Modulation electricity input, and Fig. 3 B is the polar plot in output place of PI phase shift Mach-Zehnder modulator, has illustrated that how using the AC compensating signal to offset the thermal induction index moves and cause the output of bilateral AM optics.
Fig. 4 is used to illustrate the block diagram of the controlling schemes of PI phase shift Mach-Zehnder modulator according to the preferred embodiment of the invention.
Fig. 5 shows the step that the controller by the operating set-point that is used to control Mach-Zehnder modulator carries out or the flow chart of logic.
Fig. 6 shows the flow chart of performed step of controller or logic, is used to control the compensating signal of Mach-Zehnder modulator.
Fig. 7 shows the example of the amplitude that changes the AC compensating signal, moves with explanation overcompensation and undercompensation thermal induction optical index, so that give the MZM biasing, makes its distance can obtain the principle of the point (right axle) of High Extinction Ratio in certain controlled quentity controlled variable.
Embodiment
In the description of preferred embodiment,, and illustrate by the mode that the specific embodiment that the present invention can implement is described in the accompanying drawings below with reference to the appended accompanying drawing that forms its part.Should be appreciated that and in not departing from scope of the present invention, can utilize other embodiment, can change by implementation structure.
The present invention is the improvement controlling schemes that is used for semiconductor MZM when having electric absorption.This improvement controlling schemes comprises as the use of the AM drive signal of the electricity input that is input to semiconductor MZM and two ancillary relief signals that produce by the bias voltage controlling schemes.
First compensating signal, it is direct current (DC) compensating signal, has compensated the evenly heat that the DC component by electricity input caused and has induced index to move.Second compensating signal, it is for exchanging (AC) compensating signal, and the transient heat index that has compensated the AM component of importing as electricity especially moves, and explains as Fig. 2.As a result, AC compensating signal and AM component have same frequency and with its homophase or out-phase, this depends on the type of MZM, has wherein applied the slope of gain controlling of the amplifier-driver of the arm of AC compensating signal and MZM.In addition, the frequency of AC compensating signal must be slower than the frequency of the thermal time constant of MZM.
The DC compensating signal is applied to the first arm of MZM, and the AC compensating signal is the sinusoidal signal that is applied to the first arm or second arm of MZM simultaneously, and wherein the AC compensating signal makes the heating effect that causes owing to optical absorption invalid.The average light electric current that produces in the amplitude of AC compensating signal and the first arm is proportional, and wherein proportionality constant is determined by calibration.In addition, proportionality constant can be calibrated with except the compensation thermal effect, goes back compensating distortion (non-sine) transfer curve.In other words, proportionality constant allows our controlling schemes to operate away from point, and this point may need other parameter (for example warbling) relevant with transmission of optimization.As described in next part, the combination of AC and DC compensating signal will cause the correct generation of error signal, the bias point control of the MZM when this signal is suitable for having the optics electric absorption.
The polar plot that Fig. 3 utilizes PI phase shift MZM (PI-phase-shifted MZM) shows operation principle of the present invention as an example.Fig. 3 A is the figure of AM electricity input, and Fig. 3 B is the polar plot in output place of MZM, and the effect of AC compensating signal.The figure of Fig. 3 A and 3B draws in the mode that principle of the present invention is described intentionally, shows for electricity input, and laterally phase place is less than PI and have high AM index, and induces after index is provided by the compensation of (being provided by the DC compensating signal) at evenly heat.The electric field of the light wave of M0 arm is passed in the vector representation that is labeled as M0, and this arm is the arm that is applied in modulation signal in this case.The electric field of the light wave of MP arm is passed in the vector representation that is labeled as MP, the additional PI phase shift about the M0 arm of its accumulation in this arm.Illustrate equally in the drawings be when voltage is applied to the M0 arm electric field with the amplitude locus 300 of crossing.As the result of voltage induced optical absorption, this track 300 has the amplitude that reduces.
The compensation of evenly heat component (DC compensating signal) is simply and not to be further explained.
Point (A), (B), (C) and (D) be marked in the AM input shown in Fig. 3 A, their respective vectors is shown in Fig. 3 B.As the result of the voltage transitions of from (A) to (B) (or accordingly from (C) to (D)), the effect that the thermal induction index moves is vector (B) and (D) is converted into (B ') and (D ') respectively.As can be seen, as vector (C) and (D ') when almost overlapping each other, the output of MZM optics has one-sided AM from Fig. 3 B, and B ' and A then are not like this.In the MZM controlling schemes, use the AC compensating signal to compensate these heat numbers and move through following mode: (D ') moved back to (D), or vector (MP) is rotated to (MP ') so as (B) and the angle (MP) always equal angle between (B ') and (MP ').The former is corresponding to applying compensating signal in the arm identical with M0, and the latter is equivalent in the MP arm and applies compensating signal.The both has realized producing the identical result of bilateral AM optics output.
Fig. 4 is the block diagram that is used to illustrate the controlling schemes that is used for PI phase shift MZM400 according to the preferred embodiment of the invention.MZM400 comprises optics input 402,1 * 2 multi-mode is interfered (MMI) coupler 404, relative to each other have 0 ° or 180 ° of (PI) phase delays or two mobile modulator arm 406 respectively, 408, the M0 electrode 410 on the arm 406, the M0 phase potential electrode 412 on the arm 406, MP electrode 414 on the arm 408, MP phase potential electrode 416 on the arm 408, and 2 * 2MMI coupler 418, it is the output of MZM400.Two outputs 420,422 of 2 * 2MMI coupler 418 are called MZ_OUT_OPTICAL420 and DATABAR_TAP422.MZ_OUT_OPTICAL420 also is switched to the output that is called TAP_OPTICAL424 by optics.
Controlling schemes for MZM400 realizes in bias control circuit, this bias control circuit produces and is used to offset by MZM400 at its compensating signal of interfering thermal induction index that is caused of arm 406,408 places experience optical absorption to move, and the operating point that wherein has required emission characteristics selects to be used for MZM400 arbitrarily by overcompensation or undercompensation thermal effect.This bias control circuit is a control loop, and it comprises that controller 426, photoelectric detector 428, amplifier 430, current source 432, radio frequency modulator driver 434, capacitor 436, photoelectric current detect resistor 438, amplifier 440, bias voltage T shape inductor 442, amplifier 444 and oscillator 446.Bias control circuit operate in following more detailed description.
Controlling schemes is used AM RF input signal, and DC compensates respectively in M0 potential electrode 412 and the injection of MP electrode 414 places mutually with AC.Clearly, first compensating signal that bias control circuit produces is direct current (DC) compensating signal, its compensation is moved by the thermal induction index that the DC component of electrical input signal is caused, and second compensating signal that produces is to exchange (AC) compensating signal, its compensation is moved by Modulation and Amplitude Modulation (AM) the thermal induction index that component caused of electricity input, wherein the DC compensating signal is applied to the first arm 406 or 408 of MZM400, and the AC compensating signal is to be applied to second arm 406 of MZM400 or 408 sinusoidal signal.
As a result, can use following controlling schemes:
(1) the AM RF input signal that is labeled as SRF_AM_M0 is applied in M0 electrode 410, MP electrode 414 places, or is applied to M0 electrode 410 and MP electrode 414 places simultaneously.
(2) be labeled as I PHThe DC compensating signal be applied in MP electrode 414, MP phase potential electrode 416 or M0 phase potential electrode 412 places.
(3) the AC compensating signal that is labeled as SD_MP is applied in MP electrode 414, MP phase potential electrode 416, M0 phase potential electrode 412 or M0 electrode 410 places.Preferably, AC compensating signal and the AC component of electricity input have identical frequency and with its homophase or out-phase, the average light electric current of generation is proportional in the amplitude of AC compensating signal and the first arm of MZM400 406 or 408.The phasing of AC compensating signal must be offset the mode that heat number moves with it and be carried out.
As explanation of the present invention, three electrode uses as described below of MZM400:
(a) M0 phase potential electrode 412.As mentioned above, DC compensating signal I PHBe applied to this electrode 412.The evenly heat index that is caused by the information carrying signal SRF_AM_M0 that forces at M0 electrode 410 moves by coming tuning by reducing the electric current that refractive index is injected in this electrode 412.The operating point of wherein operating MZM400 is by changing electric current I PHControl, this electric current is injected into this electrode 412 by the current source 432 of control.
(b) the M0 electrode 410.As mentioned above, information-bearing AM RF input signal SRF_AM_M0 is injected at these electrode 410 places.In controlling schemes of the present invention, low frequency (F m=0.1-10kHz) voltage dithering signal (it is provided by oscillator 446) be applied to radio frequency modulator driver 434 gain to produce the AM drive signal, it carries out DC filtering by capacitor 436 subsequently.About 5% or littler typical electrical AM index enough be used for this purpose.
(c) the MP electrode 414.As mentioned above, AC compensating signal SD_MP is injected in this electrode 414.MP electrode 414 is the second modulator electrodes 414 at arm 408 places, wherein with respect to M0 arm 406, and optical waveform accumulation zero phase-shift (in conventional MZM400) or extra PI phase shift (in PI phase shift MZM400).SD_MP is the voltage dithering signal that derives from amplifier 444 and oscillator 446, and it is applied in this electrode 414 places then.This voltage dithering is used to compensate the additional heat that is caused by the AM RF drive signal SRF_AM_M0 that applies at M0 electrode 410 places and induces index to move.The phasing that is applied to the dither signal SD_MP of this electrode 414 depends on the gain slope symbol of amplifier 434 and the type of MZM400, and its type is zero or PI phase shift MZM400.The phasing of dither signal SD_MP (homophase or out-phase) and amplitude control realize by amplifier 444.
The logic flow of controlling schemes realizes at controller 426 places.Preferably, controller 426 carries out low-pass filtering and measures F mThe amplitude of the frequency component of the input signal at place.In addition, error signal controlled device 426 is used for calculating Δ I PHIn addition, S_POW is used for calculating the amplitude of SD_MP by controller 426.These and other function is described below in more detail.
Information-bearing RF signal SRF_AM_M0 is injected among the electrode M0 410, and this signal carries out Modulation and Amplitude Modulation by the signal SD_GA at 434 places, has caused optics to export the amplitude on-off keying signal that is labeled as MZ_OUT_OPTICAL at 420 places.As mentioned above, as the result of optical absorption, it is F that Modulation and Amplitude Modulation input signal SRF_AM_M0 causes speed mThe heat number of Hz moves change.This undesirable heat number moves by dither signal SD_MP and compensates, and it has been cancelled any transfer function and has moved and produce suitable AM optical signalling MZ_UT_OPTICAL420, TAP_OPTICAL424 and DATABAR_TAP422.
Frequency is F mThe amplitude of signal S_TAP measure by controller 426.S_TAP produces from TAP_OPTICAL424 or DATABAR_TAP422 by photoelectric detector 428.Controller 426 is injected into electric current I in the M0 phase potential electrode 412 by change PHSeek to minimize S_TAP.This guarantees that MZM 400 always remains on the impact point place operation of the transfer function with required emission characteristics.
Fig. 5 is with the step of controller 426 control MZM400 operating set-points or the flow chart of logic.Square frame 500 to 510 expression MZM controls start, and the bias point control in square frame 512 to the 522 expression MZM operations
In fact, start-up routine is the slope detection program, and it is provided with I PHValue so as to obtain electricity input and optics output between required logical relation (reverse or non-return).Utilize the polarity of correct output with respect to input, controlling schemes proceeds to the bias point control in the operation, and it passes through minimum frequency F constantly mThe amplitude of the signal S_TAP at place remains on object run point place with bias point.Produce correcting current Δ I PH(n) controlling schemes in the operation can be used synchronous or asynchronous detection method.Asynchronous detection scheme is represented in square frame 512 to 522, only needs small change is done in the control of the bias voltage in the operation and Fig. 4, so that content is suitable for synchronization detecting method shown in Fig. 4 to Fig. 6.
The startup of square frame 500 presentation logics.
Square frame 502 expression controllers 426 are with I PH(n) be set to preset value and connect RF modulation signal SRF_AM_M0.
Square frame 504 expression controllers 426 are measured the S_TAP at 0Hz place and this value are stored among the S_TAP0HZ (n).
Square frame 506 expression controllers 426 are with I PH(n+1) be set to following value:
I PH(n+1)＝I PH(n)+ΔI PH，Step
Δ I wherein PH, StepBe for the predetermined electric current step of start-up routine.
Square frame 508 expression controllers 426 are measured the S_TAP at 0Hz place and this value are stored among the S_TAP0HZ (n+1).
Square frame 510 is determination block, and its middle controller 426 determines whether that according to the S_TAP0HZ (n) and the S_TAP0HZ (n+1) that measure the current bias set-point has correct logical relation (non-return or reverse) between input and output.In other words, square frame 510 determines according to S_TAP0HZ (n) and S_TAP0HZ (n+1) whether slope has correct symbol.If not so, then n is increased by 1 by controller 426, and the mobile square frame 506 that returns of control; Otherwise control moves to square frame 512.
Square frame 512 is beginnings of bias voltage control in the operation.This square frame is respectively with I PH(n) and Δ I PHBe initialised to following value:
I PH(n)＝I PH，start-up+ΔI PH，in-op
ΔI PH＝ΔI PH，in-op
I wherein PH, start-upCome the I of self-triggered program PHEnd value, Δ I PH, in-opIt is the predetermined electric current step that is used for operating control.When phase current being set to M0 phase potential electrode 412, square frame 512 is also represented controller 426 measurement F mThe S_TAP at Hz place, and this value is stored in S_TAPF mAmong the Hz (n).
Square frame 514 expression controllers 426 utilize the Δ I that is provided with in square frame 512 PHWith I PH(n+1) be updated to following value:
I PH(n+1)＝I PH(n)+ΔI PH(n)
Wherein current source 432 is set to new electric current I by controller 426 PH(n+1).
Square frame 516 expression controllers 426 are measured F mThe S_TAP at Hz place also is stored in S_TAPF with this value mAmong the HZ (n+1).This square frame represents that also controller 426 is set to following value with Δ S_TAPFmHZ:
ΔS_TAPFm＝S_TAPFm(n+1)-S_TAPFm(n)
Square frame 518 is determination block, and its middle controller 426 determines whether Δ S_TAPFm＞0.If not, control moves to square frame 520; Otherwise control moves to square frame 522.
Square frame 520 expression controllers 426 are with Δ I PH(n+1) be set to following value:
ΔI PH(n+1)＝G *ΔS_TAPFm
G wherein *Be the loop gain in the operation, it is predetermined so that obtain required control loop performance, for example amount of convergence time and overbump.Next upgrades Δ I PH(n+1) realize by the amplitude that loop gain be multiply by Δ S_TAPFm..
Square frame 522 expression controllers 426 are with Δ I PH(n+1) be set to following value:
ΔI PH(n+1)＝-G *ΔS_TAPFm
Note in this case Δ I PH(n+1) next upgraded by multiply by loop gain G with-1 *Realize with the product of Δ S_TAPFm..
From square frame 520 and 522 as can be seen, by controller 426 with n increase by 1 and control move and return square frame 514.
The bias voltage control in start-up control shown in Figure 5 and operation, also need compensating signal amplitude control shown in Figure 6, and carry out this control simultaneously by controller 426.The operation independently of one another of these two control procedures (Fig. 5 and shown in Figure 6).
The increase of moving along with optical power owing to the thermal induction index increases, and when luminous power is absorbed, causes the more photoelectric current and the dissipated heat of a large amount, so the control of the amplitude of dither signal changes the amplitude of dither signal SD_MP according to optical power levels.Utilize photoelectric current to detect the optical power that resistor 438 and amplifier 440 are measured by modulator arm 406, and bias voltage T shape inductor 442 is applied to the DC reverse bias on the electrode 410.Amplifying signal S_POW controlled device 426 is used for required magnitude determinations with SD_GE in the gain controlling of amplifier 444 then, moves so that SD_MP always cancels the heat number at different optical power level place.
Fig. 6 is the flow chart that the control logic of being undertaken by the controller 426 that is used to control MZM400 compensating signal SD_MP has been described.
The startup of square frame 600 expression control logics.
Square frame 602 expression controller 426 measuring light electric currents also are stored in this value among the S_POW.
Square frame 604 expression controllers 426 are based on the amplitude from S_POW value in the square frame 602 and the SD_MP of canned data calculating in advance.Clearly, the compensation SD_MP calibration information that square frame 606 expression controlled devices 426 are used, it is stored as coefficient or look-up table.
Square frame 606 expression controllers 426 are provided with the value of SD_GE to realize the required amplitude for the SD_MP of given optical power level.
Except change SD_MP based on optical power, can weigh change wittingly by this way, promptly Zui Xiao S_TAP signal always appears at the impact point place of the transfer function with required emission characteristics.This moves by overcompensation or undercompensation thermal induction index and realizes.This technology also is applied in the situation of the MZM400 of thermal effect minimum wherein, because increase or reduce the out-phase AM signal at optics one and zero track place, thereby allow the operating point place of minimum S_TAP signal in any selected transfer function by the shake amplitude of regulating on other arms 406 or 408.
When showing overcompensation (SD_MP320) or undercompensation (SD_MP220) SD_MP, operates Fig. 7 the example of semiconductor MZM with different extinction ratios (ER).Under overcompensation and under-compensated situation, wherein the minimum value that minimized S_TAP_Fm signal is sought in bias voltage control in the operation no longer overlaps with the extinction ratio of maximum.This has illustrated and has utilized the SD_MP amplitude, intentionally MZM is biased into the possibility of operating point other operating point in addition that will cause maximum extinction ratio.
Bibliography
Following bibliography at this in conjunction with as a reference:
[1]Yuliya?Akulova，Greg?Fish，Ping?Koh，Peter?Kozodoy，Mike?Larson，Clint?Schow，Eric?Hall，Hugues?Marchand，Patrick?Abraham，Larry?Coldren，“10Gb/s?Mach-Zehndermodulator?integrated?with?widely-tunable?sampled?grating?DBR?laser，”TuE4，OFC?2004.
[2]Xun?Li；Huang，W.-P.；Adams，D.M.；Rolland，C.；Makino，T.；“Modeling?and?design?ofa?DFB?laser?integrated?with?a?Mach-Zehnder?modulator，”?Quantum?Electronics，IEEE?Journal?of，Volume?34，Issue?10，Oct.1998，pp.1807-1815.
[3]Photonics?Systems，Inc.，“Modulator?Bias?Controller?PSI?0202?Data?Sheet.”
[4]E.I.Ackerman，C.H.Cox，International?Topical?Meeting?on?Microwave?Photonics，Sept.2000，pp.121-124.
[5]Joseph?P?Farina，Scott?Meritt，Gregory?J.McBrien，“Bias?Control?for?DigitalTransmission?using?JDSU?Uniphase?External?Modulators.”
Conclusion
Now the description of the preferred embodiments of the present invention is summarized. The above stated specification of one or more embodiment of the present invention That purpose for illustration and description is suggested. Be not intended to be exhaustive or to limit the invention to disclosed precise forms. According to Above-mentioned instruction, many modifications and variations are possible. Be intended to scope of the present invention and be not subjected to this detailed description restriction, but pass through Claims limit.

Claims (21)

1. one kind for Mach-Zehnder modulator MZM provides the equipment of operating point control, and wherein said Mach-Zehnder modulator is interfered arm place experience optical absorption at it, and described equipment comprises:
Bias control circuit, it produces compensating signal, and this compensating signal is used to offset the thermal induction index that is caused by described optical absorption and moves.
2. equipment according to claim 1, the operating point that wherein has required emission characteristics is selected arbitrarily by overcompensation or undercompensation thermal effect, is used for described Mach-Zehnder modulator.
3. equipment according to claim 1, wherein said bias control circuit produces first compensating signal, and this first compensating signal is a direct current DC compensating signal, and its compensation induces index to move by the evenly heat that the DC component of electrical input signal is caused.
4. equipment according to claim 3, wherein said bias control circuit produces second compensating signal, and this second compensating signal is for exchanging the AC compensating signal, and the transient heat index that the Modulation and Amplitude Modulation AM component that its compensation is imported by described electricity is caused moves.
5. equipment according to claim 4, wherein said AC compensating signal and the described AM component of described electricity input have the frequency that equates and with its homophase or out-phase.
6. equipment according to claim 4, wherein said DC compensating signal is applied to the first arm of described MZM, and described AC compensating signal is the sinusoidal signal that is applied to the first arm or second arm of described MZM simultaneously.
7. equipment according to claim 4, the average light electric current that produces in the amplitude of wherein said AC compensating signal and the first arm of described MZM is proportional.
8. one kind for Mach-Zehnder modulator MZM provides the method for operating point control, and wherein said Mach-Zehnder modulator is interfered arm place experience optical absorption at it, said method comprising the steps of:
Produce compensating signal in bias control circuit, this compensating signal is used to offset the thermal induction index that is caused by described optical absorption and moves.
9. method according to claim 8, the operating point that wherein has required emission characteristics is selected arbitrarily by overcompensation or undercompensation thermal effect, is used for described Mach-Zehnder modulator.
10. method according to claim 8, wherein said bias control circuit produces first compensating signal, and this first compensating signal is a direct current DC compensating signal, and its compensation induces index to move by the evenly heat that the DC component of electrical input signal is caused.
11. method according to claim 10, wherein said bias control circuit produces second compensating signal, and this second compensating signal is for exchanging the AC compensating signal, and the transient heat that the Modulation and Amplitude Modulation AM component that its compensation is imported by described electricity is caused induces index to move.
12. method according to claim 11, wherein said AC compensating signal and the described AM component of described electricity input have the frequency that equates and with its homophase or out-phase.
13. method according to claim 11, wherein said DC compensating signal is applied to the first arm of described MZM, and described AC compensating signal is the sinusoidal signal that is applied to the first arm or second arm of described MZM simultaneously.
14. method according to claim 11, the average light electric current that produces in the amplitude of wherein said AC compensating signal and the first arm of described MZM is proportional.
15. the equipment of an optical modulation comprises:
Interfere the Mach-Zehnder modulator of arm place experience optical absorption at it; And
Bias control circuit, for described Mach-Zehnder modulator provides operating point control, described compensating signal is used to offset the thermal induction index that is caused by described optical absorption and moves by producing compensating signal for it.
16. equipment according to claim 15, the operating point that wherein has required emission characteristics is selected arbitrarily by overcompensation or undercompensation thermal effect, is used for described Mach-Zehnder modulator.
17. equipment according to claim 15, wherein said bias control circuit produces first compensating signal, and this first compensating signal is a direct current DC compensating signal, and its compensation induces index to move by the evenly heat that the DC component of electrical input signal is caused.
18. equipment according to claim 17, wherein said bias control circuit produces second compensating signal, and this second compensating signal is for exchanging the AC compensating signal, and the transient heat that the Modulation and Amplitude Modulation AM component that its compensation is imported by described electricity is caused induces index to move.
19. equipment according to claim 18, wherein said AC compensating signal and the described AM component of described electricity input have the frequency that equates and with its homophase or out-phase.
20. equipment according to claim 18, wherein said DC compensating signal is applied to the first arm of described MZM, and described AC compensating signal is the sinusoidal signal that is applied to the first arm or second arm of described MZM simultaneously.
21. equipment according to claim 18, the average light electric current that produces in the described amplitude of wherein said AC compensating signal and the first arm of described MZM is proportional.
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